1. Field of the Invention
The present invention is generally related to a controllable pitch propeller actuation system and, more specifically, to a system that locks the pitch of the blades of a controllable pitch propeller in position and prevents sudden movement of the propeller blades toward extreme positions if a hydraulic failure occurs in the pressurized supply lines to the control system.
2. Description of the Prior Art
Many different types of variable pitch propellers are known to those skilled in the art. Some variable pitch propellers respond to inherent forces, such as hydrodynamic forces and centrifugal forces, to affect the pitch of the blades of a propeller. Other types of variable pitch propellers are controllable pitch propellers that allow the pitch of the propeller blades to be changed through the external control of hydraulic pressures or mechanical linkages.
U.S. Pat. No. 3,003,567, which issued to Flaugh on Oct. 10, 1961, describes a combined mechanical pitch lock and pitch stop assembly. It has been recognized that hydraulically controlled variable pitch propellers must include lock means for preventing movement of the propeller blades to a low pitch position wherein no positive thrust is developed, and in some cases, negative thrust is developed, due to the centrifugal and aerodynamic blade twisting moments when an aircraft is in flight upon failure of the hydraulic control system. Among the objects of this patent are the provision of a combined mechanical pitch lock and pitch stop assembly for variable pitch propellers. The further provision of a mechanical pitch lock assembly for a variable pitch propeller which prevents movement of the blades in a decrease pitch direction under certain conditions, the further provision of a mechanical pitch lock control valve assembly for a variable pitch propeller which is responsive to the speed of propeller rotation and includes means for adjusting the speed setting of the pitch lock control means, and the provision of a mechanical pitch lock assembly including means for preventing locking operation thereof when the propeller is operated in the feathering and negative thrust ranges while permitting locking operation when the propeller is operated in the governing range.
U.S. Pat. No. 2,869,650, which issued to Fairhurst et al on Jan. 20, 1959, describes a pitch lock valve for hydraulic variable pitch propellers. It relates to hydraulically operated variable pitch propellers of the kind including a double acting hydraulic pitch change motor actuable by hydraulic fluid under pressure to adjust the pitch of the propeller. It also comprises a hydraulic fluid conduit for leading hydraulic fluid under pressure to the pitch change motor to actuate the motor in the sense to adjust the pitch of the propeller toward coarse pitch, and a hydraulic fluid conduit for leading hydraulic fluid under pressure to the pitch change motor to actuate the motor in the sense to adjust the pitch of the propeller toward fine or reverse pitch.
U.S. Pat. No. 3,067,825, which issued to Cullman et al on Dec. 11, 1962, describes a coarse pitch conduit valve and operator for hydraulic variable pitch propellers. The device relates to hydraulic variable pitch propellers of the kind including a double acting hydraulic pitch change motor actuable to adjust the pitch of the propeller blades.
U.S. Pat. 4,419,050, which issued to Williams on Dec. 6, 1983, describes a method and apparatus for controlling propeller pitch. The variable pitch propeller is controlled by a hydraulic mechanism responsive to forces urging an unsymmetrically mounted propeller towards its maximum pitch. Spring bias means maintains the propeller at minimum pitch under conditions of rest. The propeller is prevented from increased its pitch by the pressure produced on a closed hydraulic chamber until its reaches a predetermined revolution per minute speed when a centrifugal valve opens a first port and relieves the pressure in the cylinder and allows the propeller to increase in pitch. The increase in pitch opens a second port communicating with the pressure chamber, but that channel remains closed by a second valve that is normally closed but opens to response to a reduction in the throttle setting.
U.S. Pat. No. 4,781,533, which issued to Andersson on Nov. 1, 1988, describes a control system for a propeller with controllable pitch. An actuating system for a controllable pitch propeller comprises a hydraulic servo motor arranged in the propeller hub and connected mechanically to the propeller blades. Pressure medium is delivered to the servo motor, under the control of a control valve, from a pressure source which is connected to a stationary pressure medium chamber which embraces a rotatable shaft connected to the propeller and which is sealed against the outer surface of the shaft and communicates, via a radial pressure medium channel in the shaft, with an axial pressure medium channel located in the shaft and extending to the hydraulic servo motor.
U.S. Pat. No. 4,907,992, which issued to Cavallaro et al on Mar. 13, 1990, describes an oil distribution box for a marine controllable pitch propeller. The box is intended for use with a marine controllable pitch propeller of the type having a main hydraulic servo within a hub for controlling the pitch of propeller blades rotatably carried by the hub and including a directional valve actuated by a tubular valve rod extending through the propeller shaft from the oil distribution box. It comprises an outer stationary housing, a shaft received within the housing and coupled to the propeller shaft and an auxiliary servo chamber cylinder coupled to the shaft. A piston received in the servo chamber is coupled to the valve rod. Oil is supplied to the valve rod through an elongated annular supply chamber defined between the shaft and the valve rod by spaced-apart seals, a port in the valve rod opening to the supply chamber, a port in the shaft opening to the supply chamber and a journal clearance seal between the housing and shaft in register with the port in the shaft.
U.S. Pat. No. 5,836,743, which issued to Carvalho et al on Nov. 17, 1998, describes a variable pitch counterweighted propeller system with releasable hydraulic pitchlock. The hydraulic propeller system of this patent has a central hub including a stationary portion and a rotatable portion. A plurality of propeller blades are connected with the rotatable portion, wherein each of the plurality of propeller blades has an adjustable pitch and a counterweight biasing the blades in a first pitch direction. An actuating mechanism is used for adjusting the pitch of each of the plurality of propeller blades. A valve for locking the propeller blades at a last commanded pitch is further provided. At least the valve and the actuating mechanism are located on and rotatable with the rotatable portion.
U.S. Pat. No. 5,073,134, which issued to Muller et al on Dec. 17, 1991, describes a boat drive with an adjustable pitch propeller. The boat drive of the type in which a housing outside the hull of the boat and below the water level receives a hollow propeller shaft driven by a drive shaft connected to the propeller shaft by a transmission is disclosed. The hub of a variable pitch propeller is mounted on the propeller shaft and the axially extending stems which adjust the pitch on this hub are engaged by a push rod extending through the prop shaft and connected to a double acting cylinder at the opposite end from that at which the rod is connected to the stems.
U.S. Pat. No. 5,226,844, which issued to Muller on Jul. 13, 1993, describes an actuator for a variable pitch propeller. A drive for a boat has a propeller hub rotatable about a main axis extending in a normal travel direction, a plurality of blades projecting generally radially of the main axis from the hub and each pivotal so as to be of variable pitch, and respective blade rods extending axially and displaceable axially relative to the hub to vary the pitch of the blades. A stator carried on the boat downstream in the direction from the hub and nonrotatable about the axis rotatably supports a cylinder housing that is releasably connected to the rods for joint axial movement therewith. A piston displaceable along the axis in the cylinder is releasably connected to the hub for joint axial movement therewith. Pressurizable lines extending through the stator are connected to the cylinder for alternately pressurizing the piston and thereby relatively axially shifting the rods and hub.
U.S. Pat. No. 5,415,523, which issued to Muller on May 16, 1995, describes a control system for a variable pitch boat propeller. The marine drive has a propeller that is rotatable about a drive axis and has a plurality of blades themselves pivotable about respective blade axis projecting generally radially from the drive axis and each movable between a low pitch end position extending generally parallel to a plane perpendicular to the drive axis and a high pitch end position extending at a large acute angle to the plane. An engine rotates the propeller about the drive axis at a variable drive speed in a forward rotation direction. The blade axes are so positioned relative to the respective blades that on forward rotation of the propeller that blades are urged into one of their end positions. A single acting hydraulic actuator is connected to the blades and has a compartment pressurizable to displace the blades into one of their end positions.
U.S. Pat. No. 3,794,441, which issued to Johnson on Feb. 26, 1974, describes a variable pitch propeller. The Johnson patent pertains to novel means whereby the blade pitch in a propeller may be varied by employing uni-directional rotation of a propeller shaft, a portion of the power driving the propeller, and a pair of braking means. A propeller hub having a plurality of pivotally mounted blades is mounted on the propeller shaft. A blade pitch actuator member has a hub end and a brake end and extends through the propeller shaft into the propeller hub. An eccentric slider block is secured to the hub end of the actuator member and is interconnected to each of the propeller blades. An actuator gear is screw mounted on the brake end of the actuator member. Three pairs of planetary pinions are provided with each pair secured to a common shaft. The pairs are mounted on the propeller shaft in substantially parallel spaced relation to the axis of rotation of the propeller shaft. One of each pair of planetary pinions is meshed with the actuator gear and further meshed with an outer sun gear that is secured to a first brake actuated member.
The patents described above are hereby explicitly incorporated by reference in the description of the preferred embodiment of the present invention.
In a controllable pitch propeller used in conjunction with a marine propulsion system, it is desirable to provide a means that locks the pitch of the blades in position under certain circumstances when hydraulic pressure is no longer available to control the pitch of the blades. In systems that are known to those skilled in the art, sudden loss of pressure can cause the hydraulic system to force the propeller blades to extreme pitch positions with an abrupt and uncontrolled motion. This circumstance can occur when a hydraulic pressure line is ruptured or when a hydraulic pump or directional control valve fails.